Optometrical method and instrument



Filed pril 20. 1 1

N 4 1. b V u m Q 9 mm mi, Mm S Q R a m un M w NF v v w Q m B. tz. 'BRIERTON 'ET AL AV A OPTOIBTRIDM METHOD AND INSTRUMENT Sept. 25, 1923. 1,468,797

B. E. BRIERTON ET AL OPTOMETRICAL METHOD AND INSTRI JME ENI Filed April 20. 1921 6 Sheets-Sheet 2 Q. (Q a in g Mn N Q A a r .q Le .M

Sept. 25, 1923.

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B. E. BRIERTON ET AL OPTOMETRICAL M E'1 HOD AND INSTRUMENT Filed April 20, 1921 6 Sheets-Sheet l3 nun Sept. 25,1923. 1,468,797

B. E. BRIERTON ET AL OPTOMETRICAL METHOD AND INSTRUMENT Filed April 20, 1921 6 Sheets-Sheet 4- NH hN R a. HH

Sept. 25, 1923. 1,468,797

B. E. BRIERTQN ET AL OPTOMETRICAL METHOD AND INSTRUMENT Filed April 20. 1921 6 Sheets-Sheet 5 TIE- 1E1 @MW; w

'human eyes to determine the presence,

Sept. as, 1923 isnnmivirn E. BRIEETON an]; reigns n. 'rrnnnn, or nrniarnennivi, ,EtLABAliIA.

- p orrotrnrnreen ranrrnon Ann rnsrnon nnr.

Application filed April 20, 1921. Serial No. 462,822.

To all whom may concern Beit known that we,--Drs. BENJABHN'E. Bnrnnron and JAMES H. TINDER, citizens of the United States,'residing atBirmingham, in the county 'of Jefferson and State of Alabama, have invented new and useful Improvements in Optometrical Methods and instruments, of which the following is a specification;

. The presentinvention relates to improvements inthe art of examining and testing the nature and extent of optical defects thereof which req ire correction, and the primary object'of the invention is to provide an improved method and a novel and improved instrument of this character, whereby the radii of curvature of the cornea of the eye, on all meridians thereof, and including the pupillary area thereof,'may be easily, quickly and accurately measured, for the purpose of determining its refractive state or condition, so that all errors of refraction, due to anomalous refractive curvature of the cornea of the eye may be corrected by the fitting of eyeglasses having suitable lenses. The improvedmethod and instrumentprovided for carrying out 'thel same in accordance with-the present/invention, possesses the important advantages overmethods heretofore employedyincluding the method employed in the'use of the so-called ophthalmometers, that they enable the attendant to detect and measure errors of refraction due to anomalous refractive curvature of the polar or pupillary area of the cornea, which area is the most important refractive portion of the eye used in direct vision, as distinguished from the method heretofore i employed in the use of the so-called ophthalmometers which are incapable of testing or measuring the refractive power of the polar or pupillary area of thecornea, their tests or measurements being confined to the peripheral area of the cornea. and it being left to supposition that the polar or pupillary area of the cornea has the same refractive characteristics as those of the peripheral area. It sometimes occurs, however, that the peripheral area of the cornea may be astigmatic iniits curvature,-due, for example, to cicatrization following removal of a'foreign body or an operation, while thepupillary areaof the cornea may be normal or perfect I in its cur a u e, and vice versa, and so, Whi e determinationsmade by the use of an oph thalmometer are likely to be erroneous, due

to a false supposition on which they are based, the method'and instrument provided by the present. invention enablethe attendant to actually test and measure the curvature of the cornea, not 'only with respect to its peripheral portion, but with'respect to its most important or pupillary area and such tests and measurements may be made with facility on all meridians of the cornea.

Another object of the inventionis to provide a novel and improvediconoscope which forms part of the instrument, and which embodies a short-focus optical system capabio of presenting. greatly magnitied images from the eye to the observer, the optical system being so constituted that these images will be erect and unperverted, thus enabling the user ofthe instrument to survey the area ofthe cornea without confusion, as'any dis- I tortion that may be present will appear to the observer looking through the iconoscope V in the same relation to the poleof the cornea as such images would'app'ear' if such images were viewed directly by the observers eye, and the iconos'cope embodies an objective lens which is adjustabl'e'to vary its-magnifying power and its field, thus enabling the polar area and also the peripheral' area of the cornea-to be surveye The iconoscope also embodies prisms which constitute image-doubling elements, these prisms being adjustable to vary theimage-do'ubling effect thereof, without, however, altering the distance of the luminous objects or mire-boxes from the eyeunder observation, 'and'these] prisms are also rotatable lnlllllSOil wlth the p jects'or mire boxes remains constant. V i 7 Further ob ects of the invention are to rov1d e the relatively ad ustable elements of the between the prisms and theluininons ob instrument with scales which will directly indicate the refractive measurements deter mined bythe'xinstrnment, the mer dians on which such measurements-are made and the degree of separation of the mire boxes,fto

p ide an improved construction and'arrangement of the mire boxesorluminous obgects and the adyustment therefor, and to:

otherwise provide "a generally improved strument of this class, to the ends that the necessary tests and measurements may be rae Iii the accompanying drawings Figural is a side elevation, partly tion, of an instrument constructed cordance with the present invention;

Figure 2 is a top plan view otan iconoscope forming part of the instrument shown in Figure 1;

Figure 3 represents a longitudinal section on an enlarged scale of the iconoscope and the cooperative ophthalmostat;

Figure-4 is an elevation of the radiant boxes, as viewed from the side thereof which faces the ophthalmostat; l Figure 5 represents a section on the line 5,5 of Figure 3, looking in the direction of the arrows; a

Figure 6 represents a section on the line 6-6 of Figured;

Figure 7 is a view partly in elevation and partly in section, showing the connection and adjustment between the iconoscope bracket and the base or stand on which it rests;

Figure 8 represents on an enlarged scale a sectionron the line 88 of Figure 3;

Figure 9 represents, on an enlarged a section on the line 9-9 of Figure 1;

Figure 10 is a diagrammatic view showing the course of the light rays in passing through the optical system of the instrument; 7

Figure 11 is a diagrammatic view showing the course of the light rays from the cornea through the objective lens and image-doubling element of the iconoscope;

in acscale,

Figures 12, 13 and l l are diagrammatic views illustrating the manner in which the power of the objective lens and the imagedoubling pisms of the iconoscope are varied;

- Figures 15 and 16 are diagrammatic views showing the directions of the light rays from the mire boxes to the objective lens of the iconoscope, when the mire boxes are in touch to survey the polar or pupillary area and separated to survey the peripheral area, respectively, of the cornea;

Figures 17 to 2d inclusive represent graphically the images as they appear to the attendant in testing and measuring corneal sur- :taces having different optical characteristics The invention is carried out by the aid of an instrument of suitable construction, it being preferable to employ an instrument substantially like that shown in the drawing.

The istrument, as shown, is provided with a support which consists preferably of v a stand 1 having a broad base 2, the columns otthe stand being tubular to receive telescopically a post 3. This post supports the,

in secopthalmostat and the apex of the iconoscope to be brought to the proper'elevation. A

compression spring 4 may be advantageously placed in the tubular column of the stand, so that the bottom of the vertically movable post 3 will rest thereon, the spring substantially balancing the Weight of the instrument, and a rack and pinion adjustment 5 is preferably provided between the stand and the pillar or post 3 for adjusting the elevation of the instrument. The top of the post 3 has a head 6 fixed thereon and this head has an arm 7 rigidly secured to it, the outer end of this arm being bent or curved upwardly and provided at its extremity with an ophthalmostat 8, against'which the eye to be examined is placed. A geniostat 9 is also carried by the arm 7, it comprising a rest 10 for the chin of the patient, and a'lever 11 which is pivoted'a-t 12 to the arm 7 and provided with athumb-screw or other suitable adjustment 13on the downward extension 14, wherebythe geniostat may be positioned at the proper elevation to insure cor+ rect centering of the patients eye in the o'phthalmostat.

The iconoscope which arm 7 is supported preferably by a bracket 15. In order'thatthe iconoscope may be adjusted in a direction toward and from the ophthalmostat or the purpose of placing the opticalsystem of the iconoscope at the is located above the proper focal distance from the pole of the to the end of the arm 7, it extending across the end of the groove 17, and an adjusting screw .19 1S threaded in the block and has an operative connection wlth'the base 16.

The iconoscope, according to the present invention, comprises-a lens tube 20 which contains positive lenses 21 and 22 which com prise the first or eye-piece set of the ocular system, the positive lenses 23 and 24 which comprise the second set of the ocular system, and an achromatic objective lens comprising pr ferably a plus crownglasslens 25 which is fitted in the forward end of a second lens tube 26, and a minus fiint-glass lens 25 which is fitted in a hood 2?, the latter hay mg a threaded or other sultable form ofconnection with the forward end of-the lens tube 26 whereby it may be adj ustedaxially thereof and thus vary the distance between the ele and 25 of the achromatic lens, the purpose of which will hereinaf er appear A prisms tube being slidable longitudinally or stop or diaphragm 28 is interposed between the lenses 21 and 22 and a similar, stop or dia phragm 29 is interposed between the lenses 23 and 24. Chambers 30, 81 and 32 are the vacuum chambers of the ocular system, The lens tube 20, which contains the'lenses composing the eye-piece elements otthe ocular system, is adjustable axially relatively to the supporting bracket 15, ,a-rack and pinionadjustment 33 being preferably provided,

thepinion being supported by the tube 26' and cooperating with a rack on the sleeve 35, the latter being connected to the forward end of the lens tube 20 and slidablelongitudinally within the tube 26; The rear end of the tube 26 is steadied or supported by a sleeve orcollar 36 which fits around its rear end and is fixed as at 37 to the rear arm or fork of the bracket .15. The hood 2? which is preferably of tunnel or contracted form, is provided for the'purpose or" admitting the effective rays only to the objective lens of the iconoscope.

The iconoscope-provided by thepresent invention comprises the short-focus optical;

s stem above described in combination'with 0 j I a a rlsms or eoulvalent means for doublin the images reflected from the cornea of the eye under examination and as viewed by the observer, and, furthermore, the doubling,

power of these prisms can be varied at will byrthe observer. Moreover, the optical sy tem of the iconoscope is such that it enables the observer'to view grea ly magnified images as reflected from the eye under examination, without inversion or perversion of these images. Preferably and as shown, the tube 26 contains a prisms tube 38," this axially in thetube 26 and carrying at its forward end a pair of prisms 39 and 40,"

these prisms being reversely arranged in the tube 38 and operative to double the lmages from the respectiveihalves of the cornea of the eye under examination. Preferably and as shown, the prismstube 88 is adjustable by a rack 41 which is fixed to sa1d tube and cooperates with gears 42 and 43,-these gearsbeing mounted on a bracket 44 and the gear 43 being fixed to an adjusting shaft 45 which is provided at its outer'end with a milled head, or other suitable manipulating portion &6.

The mire boxes 27 and l8, which provide the luminous objectseator the respective sides or halves of the eye under examination, are

located at opposite sidesvot the axis of the: iconoscopebut are capable of being rela tively adjusted so as to bring the inner or proximate edges of these mire boxes into toucln'as well as to permit separation'thereof. In the present instance, these mire boxes are supported and guided to move relatively in a direction toward and from one-another,

by the track 49, the boxes being attached to carriers .50 mounted tofslide on the track 49 and held in cooperatlve relation therewith by suitable means, such for example, as by shouldered screws 51, the box 47being guided by the, screws 51- which extend through slots in the back of the box, thence through slots 52 formed-in tne boxcarriersi 5G, and thesescrews 51 aretapped or other wise fixed. in the supporting and guiding track 49. Similarly,'screws 5e may be provided which extend through slots in the back of 'the "mire box.

55 in the mire box-carriers 50, these screws being tapped or otherwise secured in the track 49. By this constru tion, the mire boxes are so supported by the screws 51 and 48' and through slots 54 that the boxes may :be adjusted toward 8 member 58 which is preferably in the fo'rm of a hand-wheel. Obv1ously,'rotat10n of the hand-wheel and,in consequence, thegear 57,

will cause the mire boxes to shi tsimulta neously n a d rection toward or from one. another and to equaljextents w1th respect to,

th optical axis of the iconoscope, the handwheel 58 and gear '57 belngmountedboncentrically of the iconoscope. In the present instance, thehand-wheel. 58 is mounted."

to revolve on a sleeve 59 to whichfthe track 49 is fixed, the-sleeve 59 'surroundmg' a sleeve 59 the latter beingrotatablyvmount-c j ed on the tube 26 0f the'iconoscope,-this sleeve 59 having collar 60 'iixechthereonie bearing" and arranged to abut against tl formed ln the upper end of the forward bracket 15. The hand-wheel 58tis provided with a suitably graduated scale 61 to cooperate with a pointer 62 attached to the sleeve 59, whereby the distawe'between, the mire boxes-will be indicated;

The collar 60 is llS also provided with a; suitably graduated 7 scale 63 to cooperate with a pointerG l which o is fixed on top of the forward end o iithe." bracket 15, whereby the angulanposltion of P20 rotation ot'the mireboxes about theaxis of.

the iconoscope'will be indicated, mount mg tllQ'HilFG'bOXBS ln the mannerdescribed,

it will be understood that'these mire boxes are not only ad'j'ustable-inadirection toward; or from one anothenfbut that they are bodily'rotatable about the optical axis ofthe iconoscope asa center, n'idependently of the adjustments 'otthe relative distance between the boxes. -The milled head; at

l'med as a handle inthe operations of rotating the mire boxes about the axis of the iconoscope. The sleeve 59 to which the mire box-supporting tracl; l9 1s fixed, and on "which the hand-wheel 58 is independently tered relation with the mire boxes;

The front each mire'box is covered with a panel 65 composed of opal or ground glass, or other appropriate translucent material, the face of each panel having a spherical sur face'which is concentric with the center of curvature of the cornea of the human eye. For example, taking the radius of curvature of the cornea at 7.8 mm., every point on the surface of the panel of each mire box would be 111; inches from the corresponding radial point on the cornea. The panels of the mire boxes also bear .on their spherical surfaces objects which are preferably in the form of opaque lines, each object shown in the present instance comprising a principal axis defining line 66 and a pair of parallel equally-spaced lines 67 at oppositesides thereof. The lines constituting the object on one panel are in alinement with the corresponding lines constituting the object on the other panel and, moreover, the lines on both panels have the same characteristic relatively to the cornea of the eye, asis pos sessed by the surfaces of'the panels; that is to say, every point on any one of these lines is the same distance from the corresponding radial point on the surface of the cornea. This characteristic insures the production of images in 'miniature which are exact facsimiles of the objects on the mire boxes, these images undergoing no distortion when reflected from the surface of the cornea, as-

suming that the surface of the cornea is normail or perfectfollowing the fundamental law of optics that every angle of reflection is equal to its corresponding angle of incidence. It is to be understood that the track 49 which supports the mire boxes is curved concentrically with the curvature of the surfaces of the panels of the mire boxes, in order that the concentric relationship between the surfaces of the panels of the mire boxes and the cornea of the eye "in the ophthalmostat will be maintained, irrespective of the relative distance between the mire boxes. 'The objects borne by the panels of the mire boxes may be rendered luminous by electric lamps 68, orot 181" suitable illuminating means.

It is to be understood that the luminous or mire boxes are located at opposite sides of the optical axis of the iconoscope and they are capable of being brought into touch; that is to say, they may be r owed toward one annaseyrev other until their proximate edges abut. To enable this to be accomplished, the inner or proximate sides of the luminous or mire boxes are recessed, as 69 and 70, so that these recesses, which are complemental to one another, will accommodate the tube 26 of the iconoscope between the luminous or mire boxes when the latter are brought into touch. I i

The optical system of the instrument functions as follows :Figures 15 and '16 each show the course of the light rays from one of the mire boxes to the cornea of the eye and thence into the iconoscope, the mire box as represented in Figure 15 being in its proximate position, while the mire box as represented in Figure 16 is in its separated position. provided by the mire box face is designated X, 1 represents the incident light rays from the luminous object, C represents the cornea of the eye under examination and 1 represents the reflected light rays from the cornea, and 25 and 25 the lenses whichin the present instance comprise the objective ofthe iconoscope. The rays 1" are reflected from the surface of the cornea at an angle which is'equal to the angle of incidence of the rays 7', although the reflected rays emanate from an image which is produced behind the front surface of the cornea which acts as a re-' flector, and this law of optics applies when the mire boxes are in touch, in accordance with Figure 15 or are separated in accordance with Figure 16, although the angle of the reflected rays relatively to the opticalaxis G() of the iconoscope will be altered, as will be clear from a comparison of Figures l5 and 16. V v l The rays 7" reflected from the cornea int the iconoscope pass through the objective thereof substantially as shown in Figures 12 and 13, the objective system' as shown being composed of theplus or positive crown-glass lens 25 and the minus flint-glass lens 25, the two combined producinga short focus achromatic lens system the dioptral power or focal length of which may be increased or do creased and also the field of view thereof diminished or increased, depending on the area of the corneal surface to be surveyed, by adjusting the lens 25 axially relatively to the lens 25. By this COHSQIHCt'lOD, when the lenses 25 and 25? are separated to the maxi= mum extent, say about 10 min, as shown in Figure 12, the minus lens 25 will produce the minimum amount of neutralization of the plus lens 25 and'the objective system will then have the maximum clioptral power and its field will be at the minimum. The obj ecarea of the cornea, which is the most useful portion of the cornea used in vision, to be in each instance the luminous objectdetermine whether the remainder of the cor-,

neal surface deviates in its curvature from that of the pupillary area, theiield of examh, nationand measurement is extended or enlarged by bringing the minus lens 2-5 closer to the pluslens 25, as shown in Figure 13, this having theefiect of reducing the power of the objective system and wideningits field to include the periheral, as well as the pupillary, areas of the cornea. V

These reflected rays 0* after passing through the achromatic objective system, pass through theimage-doubling prisms 39, asshown substantially in Figures 11 and 1 1-. v The doublingpower of this prism system is regulated by adjusting the prisms toward and from the objective'lens system,

and this prism system functions to double.

each li 'ht ray or cone of light rays from the posterior surface-of the plus lens 25 of. the objective system so that as these rays proceed to the focal distance'of-the objective system, a pair of double images of the corheal-images is formedh That is due to the fact that the prism system divides the objective lens system into two fociforming centers, Figure 11 illustrating how each ray from the prism system is split 'into two rays r which diverge as they proceed from the prism system. The double images formed at the focal distance F of the objective (Figure 10) are inverted, and these double inverted images becoming the objects project divergent rays therefrom which are received by the first lens 24 of the ocular system comprising the eyepiece, and as these rays pass through the lenses 23, 22 and 21 of the eyepiece, they are brought into parallelism, as shown diagrammatically in Figure 10, and these parallel rays fall upon the cornea of the eye of the observer or at tcndant, the latter perceives erect or uninverted, unperverted, magnified and double images of the corneal images from the eye under examination.

The image-doubling prism system is employed forthe purpose of locating the axis of the principal meridians of the cornea, and also this prism system operating in conjunction with the adjustments of the mire boxes from proximate to separated relation enables the radii of curvature of the corneal surface on these meridians, when the samehave been located, to be measured in diopters.

It will be understood, 'however, that the prism system maybe employed 1ndependently of the adjustment of the mire boxes,

and vice versa, as well as one of the elements in conjunction with the other.

The ad ustment of the prism systemto vary the distance between it and the achromatic objective system, as will be understood from Fi ures :11 and 14:, varies the image,

doubling power of theprismsystem.

The instrument hereinbefore described is operated in substantially the following mannor in testing the cornea of the human eye;

to detect errors of refraction due to anomalous refractive curvature and for measuring the amounts of such errors: The eye of the patient is placed in the ophthalmostat" 8 and the geniostat or'chin rest is adjusted so that th eye under examination will be centered in the ophthalmostat and jmaintained insuch position during the exzmnina:

tion. The operator who may be seated'at the opposite'end of the instrument, places his eye to the eye-lens 21 and, if necessary,

manipulates the, screw. 19 to bring the ocular system of the iconoscope into proper focal relation with the pole or center of the cornea fthe eye positioned in the ophthalmostat.)

Also the rack-and pinion 33 is manipulated; to focus the optical system comprising the tubefQO and the lenses 21, 22, 23and2i in the ophthalmostat, it being understood that this adjustment of the iconoscope is ef-- footed without altering the distance between the faces of the mire boxes and the surface of the cornea ofjthe eye positioned, in the ophthalmostat The lampswithin the mire boxes being illuminated, the objects on the translucent panels of-these boxes will produee images which will be reflected bythe boxes are at the proper distancefrom theeye under examination, every point on'such faces is equi-distant from a corresponding point on in the ophthalmostat,it-follows, in obedience to the law of optics that the angle of re-- ilection is equal to the angle rofincide'nce, that each light ray. emanating froinjthe luminous face of each mire box will travel unequal distance to reach its corresponding point on the cornea of the eye, in consequence of which images of themire box faces will be reflectedfrom the cornea which will; be free from metamorphopsia or distortion. These reflected images, while they are of miniature size when reflected from the cornea, appear as greatly enlarged images in theg eye of the ob server, due tothe short-focus optical system of the iconoscope. Moreover, these images visible; to theobserver, are erect or r relatively to the cornea of the eye positioned 2 the cornea of the eye positioned surface under examination.

Lin-inverted andv they are ail-perverted, so that the relation of the images to the pole or center of the cornea, as they appear to the observer, corresponds to the actual position of these images as they would appear in the cornea if observed directly by th eye of the observer. 7

The prism system 39 comprising part of the optical system 01": the iconoscope, constitutes a constant image-doubling element, and its adjustment in a direction axially of the ocular system ofthe iconoscope is for the purpose of determining the curvature of the corneal surface on'its diilerent meridians by finding the amount of prism power required to completely double the images as they are seen through the iconoscope, it being understood that the mire box system employed will produce corneal images which are perfectl hat touch independently 01" the prisms.

Commencing the examination with the mire boxes at touch and set horizontally and with the prism system set at zero, the double images observed bythe attendant will be like those shown in Figure 19 if the cor- .nea under examination is emmetropic or normal. If the curvature is myopic and the mire boxes are separated slightly, the observed images will appear like that represented in Figure 17 or Figure 18, depending on the degree of departure from normal, whereas if the curvature is hypermetropic or hyperopic and the mire boxes are sepa rated slightly the observed images will appear like that represented in Figure 2G or Figure 21, depending on the degree of departure from normal. In any one of these cases, the curvature of the corneal surface under examination may be measured and de termined, in diopters, by adj usting the prism system 89 from its zero or neutral position, in the proper direction until the double im ages under observation appear like those shown in Figure 19, when the mire boxes are in touch the adjustment of the prism system being effected by turning the knurled knob 46, and the amoun of prism power required to correct the anomalous refractive curavture will be indicated, in diopters, on

the scale 72.

Figure 22 shows how the double images would appear to the observer when the increased. doubling power of the prism system is used and the radiant boxes are separated to a substantial extent, the intermediate space in this image being produced by the increased doubling power of the prism system and the lateral spaces by the separation or the mire boxes. I

Should the images observed by the attendant appear like those shown in Figure 23, it would indicate astigmatism in the corneal The mire box system together with the iconoscope would then be revolved, while. the images remain under observation, until the lines of the double and their components are in exact alinement, and having located such meridian,

the axis oi: which will be indicated by the scale andpointer' 63 and 64, the amount of ametropia of the eye due to anomalous curvature of the cornea thereof is measured, after which the mire box system and iconoscope will be rotated to a position at right angles to its former position, thus bringing the imagesinto the meridian corresponding to the secondary axis, when the images will appear substantially like those shown in Figure 2%, wherein the longitudinal lines of the images and their components are in alinement but the central portion of the figure is shortened. The amount of this shortening will be measured by adjusting the prism system and the mire box system and indicated preferably directly in diopters and fractions thereof, by therespective scales of the instrument any difference observed in the size of the images on the different meridians or" the eye under examina tion will indicate the presence o1 astigmatism, whereas, if nodifierence is observed in the size of the images on the different meridians, it indicates the absence of astigmatism.

In examining the cornea of the eyeto detect' anomalous refractive curvature, and especially astigmatism, the mire boxes are shifted relatively in a direction toward and from one another, from a position where they are in touch, that is, their proximate edges are in contact, to their separated relation, or vice versa, by rotation of the handthe prism system by turning the knurled head or knob 46 until double images of the mire boxes are visible to the observer, the

amount of the anomalous refractive curva-- V ture of the cornea will be determined, and

this w ll be indicated by the scale, and

pointer 71 and 72Q-The same operation of relatively ad usting the mire boxes while the images thereof as reflected by the cornea are under observation, and, if necessary, adjusting of the prism system to produce complete double images from the respective mire boxes, is repeated on the various meridians of the eye under examination, the mire boxes and the iconoscope being rotatable bodily or as a unit about the optical axis of the icono-g scope, the milled head or knob 4:6 being conveniently utilized as a handle for this latter operati n, and'the scale and pointer '63 and 64 indicating the angle of rotation, and hence the meridian of the cornea undergoing examination. In this way, any anomalous refractive curvature that may exist on any meridian of the cornea will be detected, and the prism power required for its correction may be accurately measured.

By constructing the mire boxes as hereinbefore described, it is possible, with an 1nstrument embodying the present invention,

to examine and measure not only the peripheral area of the corneal surface,'but also the pupillary area thereof, and hence, the ex animation and determinations are scientifically correct and accurate as they are based on the actual measurements of the refractive characteristics of the most important part of the corneal surface, as distinguished from determinations based upon supposition.

The facility of the examination and the accuracy of the measurements of the corneal surface are aided by using the three par llel opaque lines on the translucent faces of the mire boxes, these lines preferably extending from the uter or remote border or edge of these faces to the opaque borders of the semi-squares 69 and 70, as these lines and the cooperative borders, forming the opaque line system, enable the exact axes of maxi-v mum and minimum curvatures to be located, by reason of the projection of these lines directly across the polar area of the cornea, and, further .iore,these lines will detect any torsion that may exist on any meridian oi the corneal surface, the central line serving to locate the axis of the meridian of the corneal surface extending directly across the pole of the cornea, and the parallel second ary lines at opposite sides thereof Wlll show the presence or prove the absence of breaks in the continuity of the curvature or distortion of the curved surface, due to cicatrization or other causes. lhe location, measurement of the diopters or refracting power, and the indication of the axes of the meridi ans of maximum and minimum curvatures are registered by the appropriate scales and pointers of the instrument, thus rendering certain the location of the meridian of astigmatism and indicating the axis and the power of the cylinder correction required where astigmatism is present.

-We claim as our invention 1. The herein described method of examining t ie' cornea of the eye for determining the refractive state of eachof the annular areas thereof and for locating the axes of proximate edges in touch from a given di-f ameter of the papillary area of the cornea under examination and causing said images l to appear to the observer as a double pair of such contiguous images, varyingthe im age doubling effect while sai double pairsof images are under observation to measure the refractive state of the central Zone of the u illar area then successivel searat- J a tral zone of the papillary area to appear to the observer as two pairsof"images which are separated to difieren't extents, and con currently varying the image doublingefiect to measure the refr ctive state of each suc- V cessive annular area outside of thecentral zone, and repeating said operations and measurements on other diameters of nea under examination.

- 2. An optical instrument, of the character described comprising ophthalm'ostat, an icon'oscope cooperative' therewith and embodying movable prisms, and mire boxes having complemental recesses in their proximate edges to accommodate the iconoscope, said mire boxes being located at oppositesides of the iconoscope and adjustable to the corbring their proximate edges into touch and.

to separate them, the prisms of the iconoscope being adjustable to conform with any of the different positions of adjustment of the mire boxes.

3. An optical instrument of the character described, comprising an ophthalmostat, an iconoscope cooperative therewith, mire boxes having recesses in their proximate edges to accommodate the iconoscope, said mire boxes beinglocated on opposite sides of. theiconoscope, and means for adjusting the 'mire boxes to bring them into different positions equidistantly from the axis of the iconoscope whereby the proximate edges of the mire boxes may be brought into touch to cause contiguous images to be reflected from V the central Zone of the papillary area of the cornea under examination and the mire boxes mayalso be brought into difierent relatively separated positions to reflect their images on theareas of the cornea outside of the: central zone of the pupillary area'and maintain the mire boxes equidistantly from the axis of the iconoscope. 4:. An optical instrument of the character; described comprising an iconoscope, and a pair of mire boxes located at opposite sides thereof and relatively 'inovable in a direction towardand from one another, the proximate. edges of said boxes, having complemental recesses to accommodate the iconoscope between them whenpsald boxes are brought into touch. 7

" borrl 5. An optical instrument of the character described comprising an iconoscope, and a pair of mire boxes located at opposite sides of its axis, the proximate etlges oi. said boxes having COIDPl-Glllfilltill recesses to accommodate the iconoscope between them when said boxes are brought into touch, and the boxes ha *ing translucent faces bearing opaque objects anti cooperative opaque 's 1 jacent to said recesses. An optical instrument of the character comprising an iconoscope and a oonerative niire boxes having opof concentric spherical curvain optical instrument or" the character ed comprising an iconoscope and a pair of cooperative mire boxes located at opposite sides thereof and having operative faces of concentric spherical curvature, and

means to guide said boxes for relative movement in a direction toward and from one another While maintaining the concentricity of their spherical operative faces.

8. An optical instrument or" the character described comprising an iconoscope adapted to be focussecl on the cornea of an eye, and a pair of cooperative mire boxes bearing obj ets all points of which are equi-distant from the same center at Which the center of curvature of the portion of the cornea of the eye is to be located.

7 In testimony whereof- We have hereunto set our hands in presence of two subscribing Witnesses. BENJAMIN E. BRIERTON. JAMES H. TINDER.

iVitnesses:

CARRIE Barron, CARL STANFORD. 

